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dc.contributor.advisorCataudella, Vittorio-
dc.contributor.advisorPerroni, Carmine Antonio-
dc.contributor.advisorMarigliano Ramaglia, Vincenzo-
dc.contributor.authorNocera, Alberto-
dc.description.abstractThe emerging eld of molecular electronics, in which individual molecules play the role of active devices, is receiving great amount of attention due to its possible technological impact. Recent advances in nanoscale fabrication and engineering techniques have made possible to study the transport properties of devices on the molecular scale. At this level, one inherently probes the quantum mechanical nature of matter which manifests a number of e ects not well understood yet. One such e ect is the mutual interaction between electrical current and molecular vibrations. The coupling between mechanical and electronic degrees of freedom in nanoscale devices is also at the heart of NanoElectroMechanical Systems (NEMS) physics. Potential applications of these systems include ultrasensitive motion detection, mass sensing, bio-molecular studies and quantum enabled technologies. In the rst part of thesis, I focused my investigation on electronic transport properties of very short molecules connected between metallic leads taking into account electron-vibration interaction inside the device with a single vibrational mode. Within two models widely used in the literature, I implemented a computational scheme for the dynamics of the oscillator mode coupled with an out-of-equilibrium molecular junction providing also a novel and more physically sounding derivation. I concentrated my attention on the physical regime where the vibrational motion of the oscillator is 'slow' with respect to all electronic energy scales and can be considered classical. I exploited the Keldysh formalism within Non Equilibrium Green's Function theory (NEGF) for the electronic subsystem together with stochastic dynamics for the vibrational degrees of freedom. As main result, the inclusion of dynamical e ects of the oscillator motion strongly modi es the physical scenario which would be obtained by a static description, even if the oscillator dynamics is much slower than the electron tunneling rate. Motivated by recent experiments on single-electron-transistor made of a single suspended carbon nanotubes, I have further investigated the renormalization e ects of the bending mode oscillation frequency of the nanotube as function of the external charge injection (due to the applied bias and gate voltages). I also included in the model the e ects of an external antenna driving the oscillations of the nanotube. Interestingly, simulations of the stochastic Langevin equation for the vibrational degree of freedom developed in the rst part of the thesis, including the e ect of the external antenna, reproduce semi-quantitatively the experimental results. I have also shown that, even in the presence of a magnetic eld applied perpendicular to the nanotube device, the nanotube dynamics can be fruitful described by a Langevin equation. In this case, the main result is that the magnetic eld provides an additional damping mechanism to the resonator mechanical motion. In the last part of the thesis, I studied electron transport through molecular systems at high injected carrier densities, where the presence of the electron-electron interactions is not negligible. I have also considered the e ect of the interaction with an high frequency molecu- lar mode (center of mass motion of the molecule) inside the device, which cannot be treated semiclassically anymore. In order to investigate systems with strong electron-phonon and electron-electron interactions, I have used an approximation-free numerical technique, suita- ble for non-equilibrium quantum many-body systems: the Density Matrix Renormalization Group (DMRG). I numerically investigated with DMRG the electronic transport proper- ties of a nanomechanical shuttling device in the Kondo regime. Nanomechanical shuttling systems (NMSS) and NEMS in general o er a unique platform for design of an electron transistor in which spin and charge transfer can be controlled mechanically. My study is motivated by recent contrasting experimental results found in the conductance measured through C60 junctions in the low temperature and low bias regime, where very small or re- latively large conductance values are detected. I focused on the e ects of tunneling barrier modulation on the electronic conductance and on the static and dynamical properties of the center of mass phononic mode, clarifying the nature of a dip found in the conductance at particle-hole symmetric point.it_IT
dc.publisherUniversità degli studi Roma Treit_IT
dc.titleElectron-vibron interaction e ects on the electronic transport through molecular systemsit_IT
dc.typeDoctoral Thesisit_IT
dc.subject.miurSettori Disciplinari MIUR::Scienze fisiche::FISICA DELLA MATERIAit_IT
dc.subject.isicruiCategorie ISI-CRUI::Scienze fisiche::Physicsit_IT
dc.subject.anagraferoma3Scienze fisicheit_IT
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